In data storage, storage device mirroring replicates data stored on a primary storage system to a secondary storage system, in order to ensure redundancy. For a storage facility comprising primary and secondary storage systems, mirroring can be implemented either synchronously or asynchronously. During synchronous mirroring, a host communicating with the primary storage system receives a write acknowledgement after data is successfully written to both of the primary and the secondary storage systems. During asynchronous mirroring, the host receives the write acknowledgement after the data is written to the primary storage system, and the data is written to the secondary storage system at a later time.
The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application.